The present disclosure generally relates to contactless three-dimensional (3D) shape measurements. More particularly, the present disclosure relates to contactless 3D shape measurement methods and devices using delay compensation in modulated optical time-of-flight phase estimation.
Contactless 3D shape measurements may use pressure wave or electromagnetic wave emissions. Pressure waves may be ultrasonic signals, for example. Electromagnetic wave emissions may be microwaves or light waves (e.g., l=0.5-1.0 um; f=300-600 THz), for example. For light wave emissions, 3D sensing methods include triangulation, interferometry, and time-of-flight (TOF). Triangulation performs depth detection using geometric angle measurements. Interferometry performs depth detection using optical coherent time-of-flight measurements. TOF may perform depth detection using either pulsed or modulated continuous-wave (CW) optical incoherent time-of-flight measurements.
Pulsed type TOF features range sensing by measuring the turn-around time, reduced influence of background illumination, high signal-to-noise ratio (SNR) with low average power for eye safety, low repetition rate (e.g., 10 kHz) of the laser diode (LD) and a low frame rate. Unfortunately, it can be difficult to form pulses with sufficiently short rise and fall times, and dispersion and attenuation can become issues.
Modulated CW type TOF features range sensing by measuring phase differences. Modulated TOF can use a wide variety of light sources, such as sinusoidal, square wave, and the like.